Altitude compensated control system and apparatus for aircraft engines



4 Sheets-Sheet l H7TORIVEY A. W. BLANCHARD ALTITUDE COMPENSATED CONTROL SYSTEM AND APPARATUS FOR AIRCRAFT ENGINES Jan. 19, 1954 Filed Aus. 2. 1951 ma UJPPDIIF zozbanz. o /okomdmm A. W. BLANCHARD ALTITUDE COMPENSATED CONTROL SYSTEM Jan. 19, 1954 AND APPARATUS FOR VAIRCRAFT ENGINES Filed Aug. 2. 1951 v4 Sheets-Sheet 2 JNVENToR. A

/77'7'UQ/VEY ALLE/v nz BLANCHARD Jan. 19, 1954 A. w. BLANCHARD 2,666,489

ALTITUDE cONPENsATEO OONTROI. SYSTEM ANO APPARATUS FOR AIRCRAFT ENGINES Filed Aug. 2, 1951 4 Sheets-Sheet 5 EFFECT OF STOP 367 R .P. M

coN'RL ALTITUDE FIG. 5

IN VEN TOR.

ALLEll/V .14. BLANCHARD Jan. 19, 1954 A. w. BLANCHARD 2,666,489

, ALTITUDE COMPENSATED CONTROL SYSTEM AND APPARATUS FOR AIRCRAFT ENGINES Filed Aug. 2, 1951 4 Sheets-Sheet 4 1777 Ole/Vd' f Patented Jan. 19, 1954 tiene g ALTITUDE TEP/I AND ENGINE S COMPENSATED CONTROL APPARATUS FOR AIRCRAFT SYS- Allen W. Blanchard, Allendale, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application August 2, 1951, Serial No. 239,971

7 Claims.v (Cl. 170-135.74)

The present invention relates to improvement in control systems and apparatus for the power units of aircraft of the type disclosed and claimed in the copending U. S. patent application Serial No. 561,083 filed yOctober 30,V 194.14 by Joel D. Peterson and assigned to Bendix Aviation Cor poration, and more particularly to an Automatic Engine Control System with altitude compensa# tion to control the power output of a single or multi-*engine aircraft over a predetermined schedule so as to adjust the power schedule with changes in altitude or the prevailingv atmospheric pressure.

An object of the inventionV is to provide an aircraft engine control` system including an engine R. P. M. control system, an engine intake manifold air pressure (M. A. P.) control system, and a turbosupercharger control system; and a system in which the R. RM. and MLA. P. control systems are coordinated over a predetermined power scheduleI by a power selection transmitter operated from a single pilots control lever.

Another object of the invention is to provide a control system in which the power selection transmitter provides a control signal for operating a governor which in turn selects the speed setting of an automatic synchronizer or power governor for maintaining the speed of the engine or engines of the aircraft at a selected value; and in which the power selection transmitter provides a control signal for operating a governor servo which in turn selects the intake manifold pressure setting of a pressure regulator arranged so as to regulate a throttle valve in the intake manifold of the engine or engines of the aircraft for maintaining such intake manifold pressure at the selected value; 'and in which control system there is further provided an altitude compensator which supplies trim signals to adjust the M. A. P. and R. P. M. setting of the respective speed governor and pressure regulator or regulators according to the prevailing atmospheric pressure or altitude.

Another object of the invention is to provide a control system for an aircraft engine having a turbosupercharger driven by the exhaust gases from the engine for maintaining a constant head of air pressure on the engine carburetor and including in the control system means for limiting the minimum selected R. P. M. to predetermined values variable with the prevailing atmospheric pressure so as to prevent instability of control of the turbosupercharger, and including further means for varying the selected yintake manifold pressure with changes in altitude so as to maintain engine efficiency at a given selected R. P. M. with variations in the Vprevailing atmospheric pressure.

it has been found that in the control of a turbosupercharger driven by the exhaust gases from an aircraft engine that if the speed of the engine is decreased below a predetermined 'value the control of the turbosupercharger becomes increasinglyr unstable with decrease in atmospheric pressure, and therefore in order to avoid such instability of control an object of the present invention is to provide altitude compensating means for increasingly limiting the minimum selected R. PJM. 'with decrease in the prevailing atmospheric pressure so as to prevent the control of the turbosupercharger from going into the aforenoted unstable' range or surging at high altitudes and low selected R. P. M.

Moreover, another object of the invention is to provide novel means to decrease the selectedinf take manifold pressure with increase in altitude of the aircraft so as to maintain high engine eiciency at a given selected R. P. M., so that the M. A. P. for the selected R. P. M. may be made to Acorrespond with a predetermined value for efficient operation of the particular engine or engines lunder. control at the prevailing atmospheric pressure. n

The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawings wherein several embodiments of the invention are illustrated by way of example.

Figure l is a diagrammatic illustration of the control system.

Figure 2 isl a schematic view of an engine system which may be controlled by the system of Figure 1. n

Figure 3 is a fragmentary plan view of a multi-engine aircraft illustrating diagrammatically the relative positions of the several operating parts and conduits carrying the electrical connections of the control system of Figure 1.

Figure is a graph illustrating a typicalv power schedule which may be maintained by the automatic power control system of Figure l, and

Figure 5 is a further graph illustrating the `operation of the altitude compensator shown schematically in Figure 1 on 'the selected R. P. M.

l Power selection trol lever' i which is adjustably positionedalong a quadrant 2 and connected by linkage 3, arm 5, shaft 'I and gearing 9 and II, respectively, to cams I3 and I5. IThe profile of the cams I3 and I5 are designed to position cam followers il and I9, respectively, so as to position rotor elements 2l and 23 of induction transformers 25 and 27 so as to translate a predetermined power schedule, such as shown in Figure 4, into electrical signals proportional to the schedule.

Figure 4 depicts a typical power schedule which may be followed by the system. As shown in Figure 4, the curve indicated by the notation Nominal Schedule represents the operating curve which may be followed by the control system without altitude compensation and is the curve that the power transmitter may translate into electrical signals at for example 12,000 feet. In such a control system the cam I3, follower I'I and transformer control the M. A. P. control system, while the cam I5, follower I9 and induction transformer 21 controls the R. P. M. control system. The cam contour of each cam i3 and I5 is cut to rotate the rotor elements 2l and 23 of the induction transformers Z5 and 2l' to the positions which correspond to signal positions for the predetermined power schedule which schedule of course is determined in part by the operating characteristics of the engine or engines to be controlled.

The rotor element 2l has a winding 25 thereon inductively coupled to a stator winding 3l of the induction transformer 25, while the rotor element 23 has a winding 33 thereon inductively coupled to a stator winding of the induction transformer 21. Both the rotor winding 29 and the rotor winding 33 are connected across conductors 31 and 39 leading from a suitable source 4I of constant frequency alternating current indicated. Thus the M. A. P. induction transformer 25 and the R. P. M. induction transformer 2l induces in the stator windings 3l and 35, respectively, electrical signals which correspond to the nominal curve of a predetermined power schedule, illustrated for example by the graph of Figure 4.

Altitude compensator A novel feature of the present invention is an altitude compensator which is designed to modify the predetermined nominal power schedule with changes in the prevailing atmospheric pressure.

vThis modication of the nominal power schedule affects both the M. A. P. and R. P. M. control systems. The altitude compensator transmits a voltage to the M. A. P. control system for adding to or subtracting from the electrical signal transmitted by the power transmitter so as to increase the M. A. P. setting upon an increase in the prevailing atmospheric pressure and decrease the M. A. P. setting upon a decrease in such atmospheric pressure. The altitude compensator also applies a control signal to a minimum R. P. M. stop or limiting means which places a minimum limit on the selected R. P. M. This limit increases with the altitude of the aircraft or decrease in the prevailing atmospheric pressure. Thus, as illustrated, for example, by Figure 4, the minimum limit at 12,000 feet may be slightly less than 1600 R. P, M. while at 30,000 feet it may be about 1760 R. P. M.

M. A. P. altitude compensator In affecting the M. A. P. control system, the compensator includes two induction transformers .454 and ill, respectively, which serve to make the aforencted'modication to the M. A. P. setting of and minus 4" of mercury at 30,000 feet.

the predetermined power schedule curve. The induction transformer 41 has a stator winding 155 and a rotor winding 5I inductively coupled thereto. The rotor winding 5i is connected through a Calibrating resistor 53 across the lines 3l and 39 leading to the source of constant frequency alternating current iii. The winding 5l is wound upon a rotor element 55 which is adjustably positioned by an ambient atmospheric pressure responsive mechanism 5l, including two sealed evacuated bellows 55, positioned in a casing Si open by a conduit '55 to the prevailing ambient atmospheric pressure. The bellows 55 adjustably positions the rotor 55 through a rod 62, arm 53 and shaft 55. Thus, the winding 5l induces into the stator winding 49 of the induction transformer 5l a signal which is proportional to the prevailing atmospheric pressure or altitude of the aircraft. This signal is applied to a primary winding 'I0 of a transformer 'i4 connected across the stator winding 5:15 and inductively coupled to a secondary winding l5 of the transformer '14. The secondary winding l5 is in turn connected across a rotor winding 11 of induction transformer 45.

The winding 'il is inductively coupled to a stator winding I5 of the induction transformer d5 and the winding l5 is connected in series with the M. A. P. signal induced in the stator winding 3i of the induction transformer 25. The rotor winding il is wound on a rotor element 8l adjustably positioned by cam follower 83 bearing upon a cam element :35 which is adjustably positioned through gearing 81, tarm S9 and linkage 5I by the main control lever I.

The contour of the cam 85 is such that when the input lever I is at a predetermined position, 1500 R. P. M., 25 M. A. P. on the power schedule of Figure 4, the coupling^ relation between the rotor winding 'I1 and the stator winding 79 is at a maximum. Thus, at such predetermined position of the main control lever I any modifying voltage from the pressure sensing induction transformer 47 is at a maximum and is of a voltage sufficient to make the necessary correction in the M. A. P. setting for the atmospheric pressureV prevailing at the altitude of the aircraft. The atmospheric pressure sensing induction transformer 41 is so adjusted that it supplies a null signal voltage at a predetermined pressure altitude, of for example 12,000 feet, as shown in the graph of Figure 4.

Hence, at this altitude the power schedule is equal to the Nominal Power schedule. If the altitude is decreased, the atmospheric pressure sensing induction transformer ill will produce a voltage that will make the M. A. P. setting increase and conversely as the altitude is increased the induction transformer 4'! will produce a voltage to reduce the M. A. P. setting. Thus, as shown for example by Figure 4, at the 1500 R. P. M. 28 point of the graph, the correction is approximately plus 4" of mercury at sea level The power schedule of Figure 4 shows that the M. A. P. altitude compensation is maximum at 1500 R. P. M. 28 and decreases to zero at the upper end of the 2400 P. M. 42.5" point and at the lower end at 2100 R. P. M. 8" point.

This reduction in compensation correction is accomplished by the cam 85 operating induction transformer 45, which transformer has a maximum coupling at a predetermined adjusted position of the control lever I, such as the 1500 R. P. M. 28 point of Figure 4 or one-quarter advjustecl position of the main control lever I, shown in Figure l. The cam 85 rotatably adjusts the rotor winding 11 of the induction transformer 45 so as to decrease the amount of correction as the lever is moved from the one-quarter position in either an M. A. P. increasing or decreasing d1- rection.

When the lever i reaches a predetermined M. A. P. increase position, such as the 2400 R. P. M. 42.5 M. A. P. point of Figure 4, the cam 85 operated rotor winding 11 of the induction transformer 45 has turned 90 and has reached a null coupling position relative to the stator winding 19. Further movement of the lever to the maximum M. A. P. position will rotate the cam 85, but as the cam contour at this point has a zero rise the rotor Winding 11 of the induction transformer 45 remains at anull coupling position and no correction is added to the M. A. P. signal. from the one-quarter position to a predetermined 'M A. P. decrease position, such as the 2100 Similarly, when the lever I is adjusted R. P. M. 8 M. A. P. position of Figure 4, the cam l yto the amplifier 93 is subject to the correction signal aforenoted` from the altitude compensator. The other end of the stator winding 3| of induction transformer is connected to one end of a stator winding 95 of an induction transformer 9B. The opposite end of the winding 95 is connected by a conductor 91 through winding 99 of a rate generator IGI and through a conductor |93 to the input of the amplifier 93.

Amplifier 93 may beof any suitable type of electronic torque amplier well known in the art or may be an amplifier of the type such as shown in U. S. Patent No. 2,493,605 granted January 3, 1950 to Adolph Warsher and assigned to Bendix Aviation Corporation.

Electrical 'conductors I 01 and |09 lead from the output of the amplifier 93 to a control winding of a two phase reversible servomotor ||4 of conventional type and having a main winding ||5 connected across the lines 31 and 39 leading from the source 4| of constant frequency alternating current. i

The motor I 14. is operatively connected through a shaft IIE, arm ||8 and link |20 to an arm |22 for Varying the pressure setting of an intake manifold pressure regulator |24. The pressure regulator i241 may be of a conventional type or of a type disclosed and claimed in U. S. Patent No. 2,508,229 granted May 16, 1950 to C. E. Cole and assigned to Bendix Aviation Corporation.

The regulator |24 senses intake manifold pressure through a conduit |25, as shown schematically in Figure 2, and is arranged to position through arm |28 and link |39 a carburetor throttle valve 3| so as to maintain the intake manifold pressure at a value selected by the positioning of the lever |22, as explained in the aforenoted Patent No. 2,503,229.

The motor I I 4, as shown schematically in Figure l, is also arranged to position through the shaft H5 a rotor element |34 of the induction transformer 96. The rotor element |34 has wound thereon a winding |36 inductively coupled to the stator winding and connected through lines |38 and |45 across the lines 31 and 39 lead- 6 ing to theV source 4| of constant frequency alternating current.

The voltage induced into the stator winding 95 of induction transformer 95 by the rotor winding |35 has an opposite phase relation to that induced in the stator winding 3| by the rotor winding 29 of the induction transformer 25 so that the one tends to balance the voltage induced in the other plus the altitude compensating voltage induced in the stator Winding 19 of the induction transformer 45, as heretofore explained.

In addition to driving the shaft ||6 the servomotor ||4 also drives through a shaft I4I the rotor of a rate generator ||l| of a conventional type. The rate generator |0I has in addition to winding 99 a second winding |43 connected by lines and |41 across the lines 31 and 39 leading from the main source 4| rof alternating current. The rate generator Iti also has its rotor driven through shaft Iii! by the servomotor I I4 at a speed proportional to that of the motor I I4.

The output from the rate generator ISI is applied across the winding 9S and has a frequency determined-by the main source 4i connected across winding |23 and the output voltage is proportional to the speed of rotation of the servornctor lit The rate generator |2|y is arranged to induce a feed back voltage having a phase relation acting in opposition to that of the resulting signal voltage from the induction transformers 25, 45 and 55 so as to prevent over-adjustment of the pressure selector lever |22 by the servomotor H4, thus giving stability of control to the system.

Manifold pressure regulator and turbosupercharger cated generall;7 by numeral |54 and adjusted through an arm |56, as hereinafter explained. There is further provided an auxiliary supercharger |65 driven by suitable driving means, shown diagrammatically in Figure 2, as a turbine |52 driven by exhaust gas from the engine |59 through an exhaust conduit |64.

The auxiliary supercharger |50 has an air inlet conduit |65 which may be connected to an air scoop Vinthe conventional manner.

There is further provided an air pressure conduit |68 leading from the outlet of the auxiliary supercharger |60 through an intercooler |19 and an air conduit III rfrom the intercooler Il'Il to the inlet of a main supercharger |l2 driven by the crank shaft of the engine |59. A carburetor |14 is provided in the air conduit ill in the conventional manner. An air intake manifold |'l3 leads from the outlet of the main supercharger |12 to the fuel-air intake of the engine |50.

The speed of rotation of the supercharger |550 and turbine |52 is controlled by a waste gate |15 in a manner well known in the art. Any other suitable driving means for the supercharger |59 may be provided instead of the turbine |62, such asan auxiliary variable speed motor means of any suitable type. l

In the instant case the waste gate |15 is adjustably positioned by a servomotor |18 through a rod |36. The motor |18 is in turn controlled by a differential pressure regulator |62 which may be of a conventional type and which senses the 'pressure drop across the throttle valve |3| through lines |83 and |84, respectively, leading from opposite sides of the throttle valve 13| to the differential pressure sensing device or regun lator |82 to control the motor |78 so as to maintain a difference between the carburetor-inlet and carburetor-outlet pressure in excess of a predetermined value.

In the system of Figure 2, the intake manifold pressure in conduit |73 is regulated by the throttle valve |3| adjustably positioned by the pressure regulator i211 which senses intake manfoid pressure changes through the conduit and opens or closes the throttle valve I3! so as to maintain the intake manifold pressure at the value determined by the adjustment of the se lector lever |22. At high altitudes.. under circumstances where the intake manifold pressure selected through operation of the lever i is higher than that obtainable with the throttle valve |31 fully open, it is necessary to increase the carburetor inlet pressure above atmospheric pressure. This is obtained through suitable adjust ment of the speed of the turbosupercharger IEB by varying the position of the waste gate |76 through the operation of the differential pressure sensing regulator |82. The differential pressure regulator |82 is set so as to maintain a difference between the carburetor-inlet and carbu retoreoutlet pressures slightly greater than that existing at fully open throttle at 'maximum power. Thus, the speed of the turbosupercharger is so regulated that the supercharger is supplying sufcient carburetor-inlet pressure to keep the manifold pressure regulator |24 within working range.

The exhaust gases from the engine liill pass through the exhaust manifold l to the turbine |22 where part of the gases go through the turbine m2. This causes the turbine to rotate and in turn drive the supercharger |69. The remaining gases are oy-passed to the atmosphere through the waste gate |76.

Air is picked up by the ram air intake |556 and passed to the varies of the impelle'r of the supercharger |66 which is driven by the turbine |52. The impeller of the auxiliary supercharger |63 compresses the air and delivers itrthrough the intercooler |75 to the carburetor ll'i where it is mixed with fuel. The air is then directed into the main engine driven superoharger |72 where it is further compressed and fed to the cylinders of the engine |52. As the altitude changes the pressure on the vanes of the impeller of the supercharger |66 increases or decreases, it becomes necessary to decrease or increase the speed of the auxiliary supercharger it to maintain the carburetor inlet pressure. This is done by moving the waste gate V73 thus changing the amount of exhaust gas driving the turbine |52.

The primary function of the differential turbosupercharger regulator |22 is to open or close the waste gate I'i automatically so as to vary the speed of the supercharger |553 so as to hold the carburetor inlet pressure constant regardless of changes in atmospheric pressure, when a constant manifold pressure throttle valve setting made, and thus to supply sufficient carburetor inlet pressure to keep the manifold pressure regulator |22 within working range.

R. P. M. selector control As heretofore explained, the 'signalthat controis the selected engine' R. P. M; `Jriginates in the power transmitter control lever through its adjustment of the rotor winding 33 of the induction transformer 27. The R. P. M. induction transformer 27 transmits an electrical signal that has a certain relationship to the position of the power lever and follows a predetermined schedule, as illustrated graphically by AFigure 4. Therefore, this electrical signal represents the definite value of R. P. M. as determined by the position of the control lever I. The output of the stator winding 35 of the induction transformer 27 is connected through conductor 22d to the input of a suitable electronic torque ampli- Y fier 202 which may be of a conventional type or of a type such as shown in U. S. Patent No. 2,493,605 granted January 3, 1956 to Adolph Warsher and assigned to Bendix Aviation Corporation. The other output of the stator winding 35 of induction transformer 27 is connected through a conductor 2M to the stator winding 2% of a second induction transformer 22d. The opposite end of the stator winding 206 is connected through a conductor 2H. and an output Winding 212 of a rate'generator 2id to the other input of the amplifier The output of ampliner 222 is connected through conductors 2id to a control winding 2li of a two phase reversible servomotor 222 having another winding 22d connected across the main source 6| of alternating current through conductors 37 and 39.

As indicated diagrammatically in Figure 1, the servomotor 222 is operatively connected through a shaft 223 and gearing 225 to a main R. P. M. control member 227 and also through shaft 222 to a rotary element 23'@ of induction transformer 2532. The rotary element 2223 has wound thereon a winding 222 connected through conductors S7 and 35i-to the main source 4| of alternating current. The winding 232 induces into the stator Winding 266 of the induction transformer 223 a voltage having an opposite phase relationship to that induced in stator winding 3E of the induction transformer 2'! so that the voltage induced in the one tends to counter-balance the voltage induced in the other and in normal balanced relationship, there is no signal or error voltage applied to the amplier 222 through the input lines 20S and 2|ll.

If, however, the governor servo induction transformer 222 is not in balanced relationship with the R. P. M. induction transformer 27 an error signal is developed. This error signal is fed through the amplifier 222 to the control winding 2|7 and is of such a phase as to cause rotation of the motor 22u in a direction to reposition the rotor winding 232 of induction transformer 25S so as to vary the induced voltage in the stator winding 256 to rebalance the voltage induced in the stator winding 35 by the rotor Winding 33' of induction transformer 27 and wipe out the error or signal voltage, while the motor 22B simultaneously repositions the R. l?. M. main control member 227 to a position determined by the adjusted position of the power control lever In addition to driving shaft 223 the servoinotor 22|! also drives through a shaft 232 a rotor of the rate generator 2 i 4 of conventional type. The rate generator 2|@ yhas in addition to the winding 2|2 a second winding 234 connected to the main source il of constant frequency alternating current through the conductor lines 37 and 3Q. The rotor of the rate generator 2 le is driven through the shaft 236 by the servomotor y22d at a speed proportional to the speed of the motor.

The output from the rate generator 2M is applied through the winding 2|2 and has a frequency determined by the main Vsource 4| connected across the winding 231i and the output voltage is proportional to the speed of rotation of the motor 220. The rate generator 252 is arranged to introduce a feed back voltage in the winding 2|2 having a phase relation acting in opposition to that of the error signal voltage so as to reduce the error signal voltage with increase in the driven speed of the motor 223 so as to retard the adjustment by the motor 226 of the R. P. M. mainl control member 221 and thereby prevent over-adjustment of the member 221, thus giving stability of control to the system.

A second member 25! pivoted at 253 is normally biased by a spring 255 in a counter-clockwise direction and into contacting relation with the main control member 221 so that the position of the second member 25| may be adjustably positioned by the motor 22S through the operation of the main control member 221. Y

The member 2id may be connected, as shown in Figure 2, by a link 251 to a speed setting arm |55 of a suitable propeller pitch governor ycontrol 15d. propeller pitch governor control iSd may be of a conventional type or may be of f a type suchV as shown in the copending U. S. application Serial No. 561,083 iiled October 30, 1944 by J oel D. Peterson and assigned to Bendix Aviation Corporation, in which the propeller pitch governor idcontrols the pitch of the pron peller blades |52 so as to maintain the R P. M.

of the engine at a value determined by the sei'- ting of the arm 15b. The arm it may be adjustably positioned through linkage 221 by the motor 22 Vand control member 221 to a position corresponding to that selected through adjustment of the cam l5 by the control lever i.

LIn an alternative form of the invention for multi-engine control, as shown in Figure 3, the member 24| may ladjustably position through linkage 251 a control arm 250 for varying the speed setting of Ia synchronizer 253 which may be of a conventional type well known in the art and including means for balancing the speed of each engine as sensed by an alternator driven by each engine and indicated in Figure 3 by the numerals 255, 255A, 255B and 255C against the speed of a master motor in the synchronizer 253 the speed of which may be varied by the setting of the control arm 250. The alternators may be electrically connected to the master synchronizer 253 through -suitable electrical conduits 251, 251A, 251B and 251C, respectively.

IServomotors 260, 260A, 260B and 260CL controlled by the synchronizer 253' through suitable electrical conduits 253, 263A, 263B and 263C, respectively, serve to adjust the pitch of the respective propellers |52, |52A, |52B and|52C controlled thereby so that each engine R. P. M. corresponds to that selected at the synchronizer 253 by the adjustment of the control arm 250.

As shown in Figure 1, electrical connectors 265 and 266 may lead from the M. A. P. induction transmitter 25 to M. A. P. control systems for the respective M. A. P. selector motors ||4A, ||4B and IMC. Each of such M. A. P. control systems may include an induction transformer, rate generator, and 'amplifier corresponding to that provided for the motor I I4 and indicated in Figure 1 by the numerals 96, |0| and 93.

VSuch M. A. P. control systems for the motors ||4, IMA, ||4B and ||||C may be housed in control boxes 261, 261A, 261B and 261C operatively connected through electrical conduits 268, 268A, 268B Iand 268C, as shown in Figure 3, to control signal.

iii box 210 and through a conduit 21| tothe M. A. P. induction transmitter 25 which may be housed in a transmitter -control box 213.

The control arm 24| is operatively positioned by motor means ,controlled by the R. P. M. control system, shown schematically in Figure 1, and housed in the control box 210.

The 'power-transmitter control including lever I, cams I3 and l5 and the induction transformers 25 and 21 is housed in the control box 213 and is operatively connected, as shown in Figure 1, to the R. P. M. control system in box 210 through the electrical conduit 21|, shown in Figure 3 and through conduits 258, 268A, 268B and 268C to f the M. A. P. control systems in the control boxes 261, 261A, 261B and 261C.

It will be seen from the foregoing, that the R. P. M. signal from the R. P. M. selector induction transformer 21 is matched against the signal from the governor servo operated induction transformer 208, the resulting electrical addition of these two signals is an error signal proportional to the misalignment between the two induction transformers. When the control arm 256 on the synchronizer 253 is in a position to select theR. P. M. called for by the power transmitter lever the signal from the R. P. M. induction transformer 21 is equal to, but of opposite phase to the signal from the governor induction transformer 208 and the resulting error signal is zero indicating that the control arm 250 of the synchronizer 253 is at the proper position to obtain the R. P. M. called for. If the governor induction transformer 208 is not in alignment with the R. P. M. selector induction transformer 21 an error signal is developed. This error signal is then applied through the amplifier 202 to control the servomotor 220 so as to effect rotation thereof in a direction such as to actuate the arm 250 to the correct R. P. M. position and reposition the rotor winding 232 of the induction transformer 208 so as to balance out the error Rotation of the motor 220 also effects through the rate generator 2 i4 a stabilizing signal which is combined with the error signal and fed to the input of the amplifier 202, as heretofore explained.

R. P. M. altitude compensator The aforedescribed R. P. M. system including the induction transformers 21 and 208 normally effects the R. P. M. called for by the position of the control lever regardless of the prevailing v atmospheric pressure or altitude of the aircraft.

As previously explained, however, the predetermined power schedule requires that the minimum selected R. P. M. be increased as the prevailing `atmospheric pressure decreases with increase in the altitude of the aircraft.

The mechanism for controlling the minimum selected R. P. M. includes the induction transformer 41 having the rotor winding 5| adjustably positioned in inductive relation to the stator winding 49 by the atmospheric pressure responsive mechanism 51, as previously explained. One end of the stator winding 49 is -connected through a conductor 30! to the input of an electronic amplifier 302 of a suitable type well known in the art. The opposite end of the stator winding 49 is connected by a conductor 305 with one end of a. stator winding 301 of Y a second induction transformer 309, while the opposite end ofthe stator winding 301 is connected by a conductor 3|| to one end of a stator winding 3|3 of va third induction transformer 3|5. The opposite end of assaiso- 1 i the stator winding 3 I3 is connected tor 3l1 to the input of the amplier 332.

The amplifier 93 may be of any suitable type of electronic torque amplifier well known in the 'art or may be an amplier of the type such as shown in U. S. Patent No. 2,493,605 granted January 3, 1950, to Adolph Warsher and assigned to Bendix Aviation Corporation.

Electrical conductors 3I9 and 32| lead from the output of the amplifier 302 to a control Winding 323 of a two phase reversible servomotor 325 of conventional type and having a main winding 321 connected across the lines 31 and 39 leading from the source 4I of constant frequency alternating current.

The motor 325 is operatively connected through a shaft 333 and gearing 333 to stop member cooperating with member 241 to limit the minimum R. P. M. that may be selected by the adjustment of the main control member 32'5 upon changes in the prevailing atmospheric pressure, as hereinafter explained. The motor 325 is also operatively connected through a shaft 33'! to a rotary element 353 of induction transformer (iid. The rotary element 343 has wound thereon a winding 34,2 inductively coupled to the stator winding 3 i3 and connected across the main source 4I of alternating current through Conductors 31 andV 33.

Further the induction transformer 339 has a rotor winding 35a inductively coupled to the stator Wind-ing 301. The rotor winding 35e is connected across the lines 31 and 33 leading to the source 4l of constant frequency alternating current. element 355 which is adjustably positioned by an ambient atmospheric pressure responsive mechanism 351, including two sealedevacuated bellows 353, positioned in a casing 333 open by a conduit 36! to the prevailing ambient atmospheric pressure. The bellows 35S adjustably positions the rotor 355 through a rod 362, arm 363 and shaft 365. A stop 361 cooperates witharm 363 to limit the adjusted position or" the winding 356 in response todecrease in atmospheric pressure reflecting an increase in altitude.

The rotor windings i and 35i! induce in the stator windings' 49 and 331, respectively, voltages of like phase, while the rotor winding 342 induces in the stator winding 313' a voltage of opposite phase and which tends to balance the sum of the voltages induced in the stator' windings 43 and 3315 by the` rotor windings 5I' and 356', respectively.

Upon these voltages beingV in an out of `balance relationship, there is applied. across the lines 366 and 3 l1 leading to the input of the amplifier 332 an error signal of. a phase such as to cause rotation of the motor 325 in a direction to reposition the rotor winding 342 so as to vary the induced voltage in the stator winding 313 of induction transformer 315 to rebalance the control voltages and wipe out the error signal, while the servomotor 323simultaneously repositions the stopv member 333 to a position determined by ther prevailing atmospheric pressure, since the transmitted signal from the induction transformers 49 and 333 represents the minimum R. P. M., which may be selected by the main control lever l for the prevailing pressure altitude. Where the R. P. M. selected by the main control lever i isl less` than that determined by the prevailing atmospheric pressure, the stop member. 335 takes over control ofthe member 2M and prevents the same under the biasing by a conduc- The winding 35,6 is wound upon a rotor i.

force of the spring 345 from following the position of the main control member 22?. When the R. P. M. selected by the main control lever l exceeds the minimum, the main control niember 3.2i controls the position ci the member 23|.

The curve characteristics of the induction transformers .19 and 309 are matched to give the desired predetermined P. P. M. limiting curve which, for example, follows that shown in Figures 4 and 5. As indicated in Figure 5, since at high altitudes relatively slight change in the minimum R. P. M. is required ior rela# tively large changes in the pressure altitude, the stop 331 is arranged to limit operation of the atmospheric pressure responsive mechanism 351 in response to changes in atmospheric pressures below a predetermined value so that under high altitude pressure conditions, the mechanism 31 solely controls the stop member 33E, as indicated graphically by Figure 5.

Operation Prom the foregoing, it will be seen that there has been provided a novel system for controlling the power output of a singie or multi-engine aircraft over a predetermined schedule, such as shown by Figure fi, and in which there is provided three major control systems; the R. P. M. system, the inanii'old air pressure (M. A. P.) system, and the turbo-supercharger system.

The R. P. M. and M. A. P. systems are coordinated over the power schedule by a power transmitter, including the lever i and induction transformers '25 and 21 operatively connected thereto.

The R. P. M. signal from the power transmitter provides the intelligence for operating a governor servomotor 226 which in turn actuates a propeller pitch governor control mech anism indicated by numeral its in Figure 2 or engine synchronizer indicated by numeral 353 in Figure 3.

The M. A. P. signal from the power transmitter provides the signal for operating the servomotor Ils for Varying the pressure setting of a boost control mechanism ld.. as shown in Figures 1, 24 and 3.

A novel feature ci the invention is the provision of a pressure altitude compensator which supplies trim signals to adjust the M. A. P. and R. P. M. signals in accordance with the prevail# ing atmospheric pressure affected by the altitude of the aircraft.

The turbo-supercharger system, shown in4 Figure 2, serves to maintain a constant head o air pressure on the engine carburetor which is in turn regulated by the boost control mechanism to` effect efficient operation oi' the aircraft engine under varying pressure altitude, and subject of course to a minimuml R; PLM. as determined by the altitude compensator.

As indicated graphically in Figure 4, movement oi the control lever i from the 1500 R; P. M. 28" M. fr. P. position to the minimum M. A. P. position effects an increase in the selected R. P.-M; to 2130 R. P. M. It will be further noted that within approximatelyvthe rst quarter range of adjustment of the control lever i, the selected R. P. M. varies inversely with the selected M. A. P., while over approximately the last three quarter range of adiustment ciAY the control lever i the selected R. P. M. varies directly with the selected M. A. P.

The aforenoted arrangement permits inl the landing of the aircraft, the adjustment of the control lever I within a first quarter range of adjustment so as to select a relatively high R. P. M. setting with minimum M. A. P. permitting in turn the propellers of rthe aircraft to windmill, i. e., to be driven jointly by the engine and force of the air through which the aircraft is flying and at the relatively high R. P. M. setting, while the engine is operating under a minimum'M. A. P. tending therebyT to decrease the landing speed of the aircraft and facilitating the landing operation thereof. f

This arrangement further provides a propeller pitch setting which will effect emergency power upon rapid increase in manifold pressure by appropriate adjustment of the lever l by the pilot without requiring a change in propeller pitch and the subsequent time delay by the propeller pitch control mechanism.

Although only two embodiments of the invention have been illustrated and described, various changes in the form and relative arrangements of the parts may be made to suit requirements.

What is claimed is:

1. For use in controlling the 'power output of an aircraft engine having an air intake pressure regulator and an engine speed governor; the combination comprising a first actuator motor to vary the pressure setting of the regulator, a master control means, means for operably connecting the master control means to said first actuator motor, atmospheric pressure responsive control means connected to said first actuator niotor by said last mentioned connecting means, including first means in said connecting means to effect operation o-f said first actuator motor from said pressure responsive control means to vary the pressure setting of the regulator with changes in altitude of lthe aircraft, and second means operably connecting the master control means to said first means to vary the effect of said pressure responsive control means on said first actuator motor, a second actuator motor, means for operably connecting the master control means to said second actuator motor, a third actuator motor, means for cperably connecting the pressure responsive control means to said third actuator motor for controlling the third moto-r with changes in the altitude of the aircraft, a member to be controlled for varying the speed setting of the engine speed governor, and means for operably connecting said second and third actuator motors to said member to adjustably position the same.

2. For use in controlling the power output of an aircraft engine having an air intake pressure regulator and an engine speed governor; the combination comprising an electrically operated nrst actuator motor to vary the pressure setting of the regulator, a master electrical control, means for operably connecting the master control to said first actuator motor, an atmospheric pressure responsive electrical control connected to said first actuator motor by said last mentioned connecting means, including variable inductive coupling means in said connecting means to effect operation of said first actuator motor from said pressure responsive control to vary the pres sure setting of the regulator with changes in altitude of the aircraft, an operative connection between said master control and said variable inductive coupling means to vary the effect of said inductive coupling means and thereby vary the effect of said pressure responsive control means onv said first actuator motor, an electrically operated second actuator motor, means for operably connecting the master control to said second actuator motor, an electrically operated third actuator motor, means for operably connecting the pressure responsive control means to said third actuator motor for controlling the third motor With changes in the altitude of the aircraft, a member to be controlled for varying the speed setting of the engine speed governor, a pair of stop members cooperating with the member to be controlled, and means operably connecting said second actuator motor to one of said stop members and the third actuator motor to the other stop member for limiting the adjustment of the controlled member in one sense by one or the other of said stop members.

3. For use with a boost control for an aircraft engine, said boost control having an adjustable member for changing the datum of said boost control; the combination comprising an electrically operated actuator motor to position said datum changing member, a master electrical control, means for operably connecting the master control to said actuator motor, an atmospheric pressure responsive electrical control connected to said actuator motor by said last mentioned connecting means, including variable inductive coupling means in said connecting means to effect operation of said actuator motor by said atmospheric pressure responsive control, cam means operably connecting the master control to said variable inductive coupling means to vary the effect of said inductive coupling means and thereby the eifect of said actuator motor on said datum changing member in response to said atmospheric pressure responsive control.

4. For use with a propeller pitch governor for an aircraft engine, said governor having an adjustable member for changing the datum of said governor; the combination comprising an electrically operated first actuator motor, a master electrical control, means for operably connecting the master control to said rst actuator motor, a second actuator motor, an atmospheric pressure responsive electrical control, means for operably connecting the atmospheric pressure responsive control to said second actuator motor, a pair of adjustable stop members, spring means for biasing said datum changing member into operative engagement with at least one of said stop members, and means operabiy connecting said first actuator moto-r to one of said stop members and the other actuator motor to the other stop member for adjustably positioning the same to limit movement of said datum changing member under the biasing force of said spring means.

5. For use in controlling the power output of an aircraft engine having an intake manifold and a variable pitch propeller driven by the engine, a control for regulating the intake manifold pressure to a selected value, a governor for controlling the pitch of the propeller so as to regulate the engine speed to a selected value, and said control and governor each having an adjustable datum changing member operative respectively to varythe selected intake manifold pressure and speed of the engine; the combination comprising an electrically operated actuator motor for positioning the datum changing member of the intake manifold pressure control, a master electrical control, means for operably connecting the master control to said iirst actuator motor. an atmospheric pressure responsive electrical control connected to said first actuator motor by said last mentioned connecting means to effect operation of said rst actuator motor by said atmospheric pressure responsive control, other means 1 a operatively connecting said master control to said last mentioned connecting means to vary the effect of said atmospheric pressure responsive control on said first actuator motor, an electrically operated second actuator motor, means for oper ably connecting the master control to said sece ond actuator motor, a third actuator motor, means for operably connecting the atmospheric pressure y responsive control to said third actuator motor. a pair of adjustable stop members, a control ele nient for adjustably positioning the datum chang ing member oi the propeller pitch governor, spring means for biasing said control element into operative engagement with at least one of said stop members, and means operably connecting said rst actuator motor to one of said stop members. and the other actuator motor to the other stop member for adjustably positioning the stop niembers so as to limit movement or the control element under the biasing force of said spring means in an engine speed decreasing sense.

6. A control device for a supercharged aircraft engine having an air intake manifold and a throttle Valve to control the pressure of the air in said intake manifold; said control device comprising in combination a boost control to vary the position of said throttle valve with changes in said intake manifold pressure, a pilots control mechanism, means for changing the datum of said boost control, means connecting said pilots control mechanism to said datum changing means for operating said datum changing means from the pilots control mechanism, atmospheric pressure responsive means, a variable inductive coupling means to operably connect said pressure rel sponsive means to said connecting means to Vary the position of said datum changing means relative to that of the pilots control mechanism with changes in the altitude of the aircraft, and cam means operably connecting the pilots control mechanism to said inductive coupling means to vary the elect of the pressure responsive means on said datum changing means With adjustment of said pilots control mechanism.

7. For use with an aircraft engine speed governor having means for varying the speed setting of the governor; the combination compris ing a nrst actuator motor, a master control means, means for operably connecting the master control mean to said rst actuator motor, a second actuator motor, atmospheric pressure responsive control means, means for operably connecting the atmospheric pressure responsive control means to said second actuator motor, a control member for adjusting the speed setting means of the engine speed governor, means for biasing said control member in a speed decreasing sense, a pair of stop members adjustably positioned relative one to the other and in and out of operative rela-V tion with the control member, and means oper ably connecting said rst actuator motor to one of said stop members and the .other actuator mo'- tor to the other stop member for positioning one or the other of said stop members into operative relation with said control member so as to limit adjustment of the control member by said biasing means in said speed decreasing sense.

ALLEN W. BLANCHARD.

References Cited in the le of this patent UNTTED STATES PATENTS Number Name y Date Re. 22,6161 Gosslau et a1. Aug'. 7, 1945 2,346,916 Halford et al Apr. 18, 1944 2,384,353 Stieglitz Sept. 4, l1945 2,474,618 Divoll June 28, 1949 2,499,376 Ferllll, Jr. Mar. '7 1950 2,532,936 Peterson Dec. 5, 1950 2,551,979 Sparrow May 8, 1951 2,555,784 Catford June 5, 1951 FOREIGN PATENTS Number Country Date 883,676 France Mar. 29, 1943 OTHER REFERENCES Ser. No. 281,825, Stieglitz et al. (A. P. C.) published May 18, 1943. 

